Staple fibers, usually 28 in long, obtained from the fleece of sheep (and also alpaca, vicuna, and certain goats). Physically,wool differs from hair in fineness and by the presence of prominent cortical scales and a natural crimp. The latter properties are responsible for the felting properties of wool and the ability of the fibers to cling together when spun into yarns. Chemically, wool consists essentially of protein chains (keratin) bound together by disulfide cross linkages.